In order to improve mechanical properties of Mg_(2)Si/Al composites,Eu element was added to mod-ify Mg_(2)Si morphology,and T6 heat treatment was used to control Mg_(2)Si morphology and precipitate strengthening phase...In order to improve mechanical properties of Mg_(2)Si/Al composites,Eu element was added to mod-ify Mg_(2)Si morphology,and T6 heat treatment was used to control Mg_(2)Si morphology and precipitate strengthening phase.Microstructure and morphology of Mg_(2)Si were observed by synchrotron X-ray to-mography and TEM,and first-principles calculations were also performed to testify the effect of Eu mod-ification.Results show that the size of primary Mg_(2)Si particles decreases and eutectic Mg_(2)Si phase trans-forms from lamellar to fibrous by Eu addition.After heat treatment,sharp angles of primary Mg_(2)Si par-ticles passivate,and eutectic Mg_(2)Si dissolves and appears to be short dot-like.Meanwhile,nano-sizedβ"phase precipitates in the matrix.For morphology of Mg_(2)Si with Eu modification,TEM results show that Eu impedes the growing of Mg_(2)Si,which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg_(2)Si{100}facet.The adsorption and suppression growing of Mg_(2)Si transform the morphology of Mg_(2)Si and thus improve the elongation.UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%,which improved 81%and 200%compared to the as-cast Al-15%Mg_(2)Si composite.The strengthening mechanism mainly results from precipitation strengthening of nano-sizedβ"precipitates in the heat-treated composite.展开更多
In the present study, the effects of mold temperature, superheat, mold thickness, and Mg_2Si amount on the fluidity of the Al-Mg_2Si as-cast in-situ composites were investigated using the mathematical models. Composit...In the present study, the effects of mold temperature, superheat, mold thickness, and Mg_2Si amount on the fluidity of the Al-Mg_2Si as-cast in-situ composites were investigated using the mathematical models. Composites with different amounts of Mg_2Si were fabricated, and the fluidity and microstructure of each were then analyzed. For this purpose, the experiments were designed using a central composite rotatable design, and the relationship between parameters and fluidity were developed using the response surface method. In addition, optical and scanning electron microscopes were used for microstructural observation. The ANOVA shows that the mathematical models can predict the fluidity accurately. The results show that by increasing the mold temperature from 25℃ to 200℃, superheat from 50℃ to 250℃, and thickness from 3 mm to 12 mm, the fluidity of the composites decreases, where the mold thickness is more effective than other factors. In addition, the higher amounts of Mg_2Si in the range from 15 wt.% to 25 wt.% lead to the lower fluidity of the composites. For example, when the mold temperature, superheat, and thickness are respectively 100℃, 150℃, and 7 mm, the fluidity length is changed in the range of 11.9 cm to 15.3 cm. By increasing the amount of Mg_2Si, the morphology of the primary Mg_2Si becomes irregular and the size of primary Mg_2Si is increased. Moreover, the change of solidification mode from skin to pasty mode is the most noticeable microstructural effect on the fluidity.展开更多
The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si com...The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.展开更多
The effects of variation of Mg content on microstructures, the tensile properties and the formability of Al-Mg-Si-Cu alloys for automotive body sheets were investigated by means of scan electron microscopy, optical me...The effects of variation of Mg content on microstructures, the tensile properties and the formability of Al-Mg-Si-Cu alloys for automotive body sheets were investigated by means of scan electron microscopy, optical metallographic analysis, tensile and Ericsson tests. The results show that for Al-Mg-Si-Cu aluminium alloys with excessive Si, with an increment of Mg content, the strength enhances, the specific elongation and Erisson values of alloys decrease, and the number of Mg2Si constituent increases and that of Al（MnFe）Si type constituents reduces. Al-Mg-Si-Cu aluminium alloys with excessive Si for automotive body sheets can present obviously the paint bake hardenability during the paint bake cycle （i.e. artificial aging at 170 ℃ for 30 min immediately after the solution treatment and quenching）. Suitable Mg content should be controlled in the range of 0.8% and 1.2%（mass fraction）.展开更多
基金the National Natural Science Foun-dation of China(No.U21A2042)the National Science Fund for Distinguished Young Scholars of China(No.51825401).
文摘In order to improve mechanical properties of Mg_(2)Si/Al composites,Eu element was added to mod-ify Mg_(2)Si morphology,and T6 heat treatment was used to control Mg_(2)Si morphology and precipitate strengthening phase.Microstructure and morphology of Mg_(2)Si were observed by synchrotron X-ray to-mography and TEM,and first-principles calculations were also performed to testify the effect of Eu mod-ification.Results show that the size of primary Mg_(2)Si particles decreases and eutectic Mg_(2)Si phase trans-forms from lamellar to fibrous by Eu addition.After heat treatment,sharp angles of primary Mg_(2)Si par-ticles passivate,and eutectic Mg_(2)Si dissolves and appears to be short dot-like.Meanwhile,nano-sizedβ"phase precipitates in the matrix.For morphology of Mg_(2)Si with Eu modification,TEM results show that Eu impedes the growing of Mg_(2)Si,which is verified by first-principles calculations that Eu atom preferentially adsorbs on Mg_(2)Si{100}facet.The adsorption and suppression growing of Mg_(2)Si transform the morphology of Mg_(2)Si and thus improve the elongation.UTS and elongation of the heat-treated Eu modified composites are 281 MPa and 8.4%,which improved 81%and 200%compared to the as-cast Al-15%Mg_(2)Si composite.The strengthening mechanism mainly results from precipitation strengthening of nano-sizedβ"precipitates in the heat-treated composite.
文摘In the present study, the effects of mold temperature, superheat, mold thickness, and Mg_2Si amount on the fluidity of the Al-Mg_2Si as-cast in-situ composites were investigated using the mathematical models. Composites with different amounts of Mg_2Si were fabricated, and the fluidity and microstructure of each were then analyzed. For this purpose, the experiments were designed using a central composite rotatable design, and the relationship between parameters and fluidity were developed using the response surface method. In addition, optical and scanning electron microscopes were used for microstructural observation. The ANOVA shows that the mathematical models can predict the fluidity accurately. The results show that by increasing the mold temperature from 25℃ to 200℃, superheat from 50℃ to 250℃, and thickness from 3 mm to 12 mm, the fluidity of the composites decreases, where the mold thickness is more effective than other factors. In addition, the higher amounts of Mg_2Si in the range from 15 wt.% to 25 wt.% lead to the lower fluidity of the composites. For example, when the mold temperature, superheat, and thickness are respectively 100℃, 150℃, and 7 mm, the fluidity length is changed in the range of 11.9 cm to 15.3 cm. By increasing the amount of Mg_2Si, the morphology of the primary Mg_2Si becomes irregular and the size of primary Mg_2Si is increased. Moreover, the change of solidification mode from skin to pasty mode is the most noticeable microstructural effect on the fluidity.
基金financially supported by the Science and Technology Program of Guangzhou,China(No.2015B090926013)Postdoctoral Science Foundation of China(No.2015M581348)+1 种基金Postdoctoral Science Foundation of Northeastern University(No.20150302)the Doctoral Foundation of Chinese Ministry of Education(No.20130042130001)
文摘The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.
基金Project(2002AA331050) supported by Hi tech Research and Development Program of China Project(0208) supportedby Science and Technology of Ministry of Education of China
文摘The effects of variation of Mg content on microstructures, the tensile properties and the formability of Al-Mg-Si-Cu alloys for automotive body sheets were investigated by means of scan electron microscopy, optical metallographic analysis, tensile and Ericsson tests. The results show that for Al-Mg-Si-Cu aluminium alloys with excessive Si, with an increment of Mg content, the strength enhances, the specific elongation and Erisson values of alloys decrease, and the number of Mg2Si constituent increases and that of Al（MnFe）Si type constituents reduces. Al-Mg-Si-Cu aluminium alloys with excessive Si for automotive body sheets can present obviously the paint bake hardenability during the paint bake cycle （i.e. artificial aging at 170 ℃ for 30 min immediately after the solution treatment and quenching）. Suitable Mg content should be controlled in the range of 0.8% and 1.2%（mass fraction）.
